Existing memories may be classified into volatile working memories such as static random access memories (SRAMs) and dynamic random access memories (DRAMs), and nonvolatile storage memories such as NAND flash memories and hard disk drives (HDDs).
The volatile memories operate at a high speed, but have a problem in that the power consumption in the standby mode is large due to the leakage current. In order to solve the problem, various kinds of nonvolatile memories are being studied. Magnetic random access memories (MRAMs), which include magnetoresistance devices, are expected to replace existing working memories since they are nonvolatile and can operate at a high speed.
The MRAMs consume large current and thus large power in write operations since they need to generate a magnetic field in the write operation. This makes it difficult to achieve low-power-consumption devices since even if the standby power consumption of the devices is small, the operating power consumption is large.
Spin transfer torque-MRAMs (STT-MRAMs), which do not need to generate a magnetic field in write operations, may reduce the power consumption. Therefore, memories that use an STT-MRAM as a last level cache (LLC) are expected to consume lower power.
The STT-MRAMs, however, use a single path as both a write current path and a read current path, and therefore have a small read operation margin. The write operation margin of the STT-MRAMs is also small since excessive write current may break the devices.